


Laws of Motion

by raspberryhunter



Category: Stargate Universe
Genre: Death References, F/M, Kalman filters, Ratings: PG
Language: English
Status: Completed
Published: 2012-07-13
Updated: 2012-07-13
Packaged: 2017-11-09 21:37:01
Rating: General Audiences
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 3,931
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/458713
Author URL: https://archiveofourown.org/users/raspberryhunter/pseuds/raspberryhunter
Summary: <blockquote class="userstuff">
              <p>In which TJ and Rush become unlikely allies, Destiny may or may not be trying to play matchmaker, engineering turns out to have its moments, Young frets, and everyone more-or-less obeys Newton's Three Laws.</p>
            </blockquote>





	Laws of Motion

**Author's Note:**

> Written for two sgu_challenge challenges: #084 Amnesty and #028 Dynamic(s). 
> 
> Many many thanks to CleanWhiteRoom for totally selling me on this ship and for a helpful discussion of TJ, Rush, and Young. Also, um. This developed as a slight AU, where Rush revealed his control of the ship in a more timely fashion than in "The Greater Good"; that episode obviously never happened in the world of this fic.

**1\. An object at rest tends to remain at rest, and an object in straight-line motion tends to remain in that same motion, unless an external force is acting upon the object.**

TJ is sitting on her heels in the grass, considering the plants growing in front of her and their medicinal possiblities, when the alien blunders into the clearing. It's one of the blue aliens, the ones that captured Rush and Chloe. "What--" TJ breathes, before her training kicks in and she leaps up to fight or run.

It is almost anticlimactic. The alien appears to have a weapon, but she disarms it easily and is able to keep it immobilized with surprisingly little effort on her part, though it still struggles weakly while making distressed noises. Both her hands are necessary, especially since the alien seems to be a bit slimy, so she can't use the radio; she hopes there's someone within range of her voice.. "Backup!" she hollers. "Any backup in the area?" Perhaps Greer will hear her --

Someone strides quickly into the clearing. It's Rush. "Lieutenant Johansen?" he questions, and then he sees the alien, and stops. Of course, TJ thinks, he's not going to be very kindly disposed towards them. "Um. Dr. Rush. Can you --" She tosses him the weapon she got off the alien. He catches it, grimaces at finding it slimy, points it towards the alien.

The alien stops struggling, though it keeps keening. TJ takes advantage of this to punch her radio, intending to call Young. "Wait," Rush says, listening. 

TJ, arrested in the middle of her motion, realizes that the alien is repeating the same two liquid syllables, over and over again. "What's it saying?" she asks.

"I don't know!" Rush yells, sounding harassed. Then he blinks. "But I know who would. Chloe."

"Of course." TJ smacks herself. She should have thought of that. "Scott," she says into the radio. "This is Johansen. Can you patch me in to Chloe? Dr. Rush and I have a... problem she might be able to help us with."

"Copy that," Scott says crisply, and they wait for a few minutes, during which the alien keeps repeating its cry. It's starting to get kind of spooky, actually, and TJ is glad when Chloe's voice comes over the radio. "TJ, Dr. Rush -- what's up?"

"Chloe," TJ says, "can you tell us what this means?" She holds up the radio to the alien, who blinks and repeats the same syllables, more slowly and distinctly, as if it's figured out what they're trying to do.

There is a small silence. " _Amnesty_ ," whispers Chloe. "That's what it's saying."

The alien makes more sounds. When Chloe speaks again, her voice has acquired a slight but strange accent, and TJ realizes she is translating directly. " _Grant this one pardon for any harm borne by you and yours. Let the prisoner go free. This one will not now covet the Fate-of-the-Music-Between-the-Stars_ \--" Chloe pauses -- "um-- I think that's the Destiny." 

The alien says something else, while Chloe listens. Her swallow is audible even over the radio. "TJ? Rush? It's asking to go to its -- _mate_ , I think the closest word would be. They crashed here in a pod, and the other one is -- I can't figure out whether it's saying _ill_ or _wounded_ , possibly illness made worse by a wound? But terminally so, either way." TJ blinks, briefly wondering the slime on her hands is actually the alien's equivalent of blood, or some other bodily fluid. Alien vomit?

She glances at Rush. He looks paper-white, like he's about to faint. "Maybe it's lying," he says, sounding almost hopeful.

"No," says Chloe flatly. "I would know." Her voice shifts again to the alien accent. " _This one swears by the stars' music not to harm the ones who give it amnesty._ "

Rush's eyes lock with TJ's. TJ knows that, improbable as it seems, Rush is having the same thought she is: They will let the alien go. And Chloe cannot be involved in this, cannot even know that they mean to do this. If Young finds out Chloe is involved in any way, he'll suspect she's colluding with the aliens, or influencing them, or worse. 

"Thank you, Chloe," Rush says, his voice as gentle as TJ has ever heard it, and snaps off the radio. TJ and Rush share another look. He jerks his head in a gesture of assent, and TJ lets go entirely of the alien. "All right," Rush says harshly to it, motioning with his hands. "Go."

The alien holds its hands out for the weapon Rush carries.

"No!" Rush barks.

The alien puts a hand to its mouth. TJ frowns. "I think it might need the weapon for hunting food," she says. She takes the weapon from Rush's unresisting hands and hands it to the alien. Too late, she wonders if she was wrong, and she waits for it to shoot them, but it merely bends at the waist and knees in her direction, something that seems almost like an awkward bow, and shambles off.

TJ slumps down to the ground with relief. Rush remains standing by her, his arms crossed. "That was idiotic, Lieutenant Johansen. Are you aware how lucky you are that we're not both dead right now?"

"I know." 

Rush considers her. "You're going to be in a lot more trouble than I will," he observes dispassionately. "Young's not going to be happy when Scott tells him about this. But I'm outside of his chain of command, for the most part. You're not. So, why do this?"

"I have oaths to other authorities than Stargate Command," TJ says, a little more sharply than she intended. Rush is right. She is going to be in trouble. But she couldn't have chosen to do anything else. "'May I never see anything in the patient anything but a fellow creature in pain...'" He gives her a thoughtful, sidelong look. She remarks, "I'm surprised _you_ went along with this, Dr. Rush. You're usually more, um, pragmatic about these things."

Rush looks away from her. "I was... unavoidably detained when my wife died," he says briefly, and she can tell it has taken a massive effort of will for him to say those words, that if they had not just done what they had, he would not be saying them at all.

"I'm sorry," she says, the words completely inadequate, she knows, but what else is there to say? She touches his hand sympathetically. 

Rush snatches it away, as if the simple human contact is too much for him to bear. "A lot has happened since then, Lieutenant," he says brusquely. He pushes past her, continuing on his way as if the entire interlude with the alien had never happened. She looks after him. Finally she shrugs and philosophically starts cataloguing more plants. She might as well get everything done that she can before Scott talks to Young and she's pulled off the planet.

**2\. The acceleration of a body is parallel and directly proportional to the net force acting on the body, is in the direction of the net force, and is inversely proportional to the mass of the body.**

Scott, of course, tells Young about the conversation with Chloe, and Young gets the whole story from TJ and Rush in a meeting that is rather uncomfortable for all three of them. But TJ has to admit that Young's solution to punishing their insubordination is scrupulously fair and even generous, given the circumstances. Young bars TJ from landing parties for the next month, which she is quite unhappy about but accepts as the natural consequence of her actions. In addition, the Colonel doesn't want to make it widely known that there might be an armed alien about -- even if there have indeed been, as the alien promised, no repercussions -- so he puts it about that TJ and Rush may have been contaminated and need to spend time in quarantine, with the understanding between them that it's something like brig time as well. Indeed TJ can't swear, especially given that she they both got alien slime all over them, that they haven't been exposed to something. 

TJ imagines that Young sees their quarantine-brig combination as painful for both of them. It's not for her, particularly. She misses the rest of the crew quite a bit, true, but she also likes to have time to herself to think, and she and Rush can mostly stay out of each others' way. She's not sure of Rush's opinion, but she gets the distinct impression he's actually enjoying being apart from the crew for a little while.

Plus which, they're allowed to have whatever equipment they request. TJ figures this is the perfect time to start making headway on all the Ancient technology that Rush's mastery of the ship has opened to her, and coaxes Greer into bringing her a kino-sled full of medical equipment. Rush looks up from his laptop as she dumps it all on the ground and starts fiddling with one of the pieces.

He's still watching her, so she decides to talk to him. "I think this does something like cut and cauterize at the same time," she says, brandishing the apparatus. "I've never gotten it to work, though. What do you think?"

"I have no idea," Rush says stiffly. "I'm neither a doctor nor an engineer. You should ask Brody."

TJ raises an eyebrow. "I should tell Brody you said that. Why're you so hard on him?"

"He thinks like an engineer, not a scientist," Rush snaps. "There are times when this is useful, true, but thinking like an engineer is simply --" she is highly entertained by watching him struggle not to say _inferior_ \-- "simply not good for solving scientific problems."

"Aren't a lot of the problems on this ship engineering problems in nature?"

"You're in the medical field, of course you'd think like that, medicine is a whole other matter entirely," he says, a bit dismissively.

TJ hides a smile. "Barely science at all, is it?"

He narrows his eyes, as if he's become aware that she's baiting him. "Well, it's not. Which is a good thing, really. I'd be rather less comfortable with going to the infirmary if I thought you were trying to do basic science instead of sticking to established protocols."

"You never go to the infirmary unless someone drags you there," TJ points out.

"This doesn't in the slightest invalidate my point."

*

TJ wakes up to see Rush hunched over a laptop, his face eerily illuminated by the glow from the monitor.

This in itself is fairly common -- it's been the sight she's woken up to for the past several days -- but -- wait, is that _her_ laptop? Rush sees her and says, almost guiltily, "I couldn't sleep, and I saw you were looking at the Ancient medical databases... I thought I might see if there was anything interesting in them."

She yawns and pads over to him. "Find anything?"

He smirks at her. "Yes. An _index._ Indexed not only alphabetically in Ancient, which isn't going to be a whole lot of use to you, but also by topic. Much more efficient than reading through for various tidbits, or pressing random buttons on the equipment, like you were doing."

Her eyes open wide. Rush has, she estimates, potentially saved her days, if not weeks, of work. "Wow. Yeah. Thanks. That'll be really helpful."

Rush says abstractedly, "There are some very interesting protocols in there, things that seem very different from the way they're done on Earth. I may have to change my mind about performing basic science in the infirmary. As long as it's not being performed on me."

TJ gapes at Rush in consternation. This time, she realizes belatedly as he grins back, he's baiting _her_. She makes a face at him.

* 

Their time in quarantine-brig is almost over. Rush has yelled at the science crew forty-one times (TJ's been keeping count in her lab notebook) and solved four urgent problems over the radio. TJ has figured out twenty of the more esoteric Ancient medical devices (she isn't counting the simple ones, like the cut-cauterization device, which are easy to understand with Rush's index) and has counseled six members of the crew with non-urgent medical concerns over the radio. She expects they're all lucky that they've been almost wholly in FTL this week and so no strange flesh-eating alien bacteria, or so on, have invaded the ship.

She's just thinking they're going to make it through without incident when the ship's artificial gravity goes wonky. The ship pitches as if it were in the ocean rather than in space. TJ, being somewhat used to unstable transport, is able to more-or-less keep her balance, but each time the ship bucks, Rush is thrown to the ground. She has to help him up, several times, and a couple of times he almost falls on her.

"Hey, it's like Star Trek!" Eli says cheerily over the radio. "Maybe we need to reverse the polarity."

"Stop talking idiocy," Rush snaps. TJ makes another mark in her lab notebook: forty-two.

"Actually," Eli says slowly, "I was just joking about reversing the polarity, but you know what, it's not such a terrible idea. Look, if we think about this as a driven damped harmonic oscillator --" 

"I don't think that's at all the right model," Brody objects. "It's more like a random acceleration, drawn from a Gaussian distribution -- you really just want a simple Kalman filter to model what's going on."

"What's a Kalman filter?" Eli asks.

There's a silence. TJ is starting to realize that both Brody and Eli are waiting for Rush to answer when Rush clears his throat and says, "Brody. Perhaps you could enlighten us."

Brody, sounding incredulous, says, "You know, the _Kalman filter_ , the standard engineering algorithm for optimal estimation with noisy data in linear systems--" He pauses, clearly waiting again for Rush to jump in, but when he doesn't, Brody keeps going: "Okay, um, so, you have your dynamics model, the control input, and the sensor measurements --" Rush, listening intently and scribbling in his notebook, raises his eyes to scowl exaggeratedly at TJ. She gives him a beatific smile in response.

*

Several hours later, Brody says finally, "I think we've got it. Brace yourself for one last jolt -- _now_."

TJ braces herself, but Rush, still holding the radio, is just a second too late, and as the ship heaves, he overbalances and falls directly onto TJ, in such a way that his face is an inch from hers, his hand curving around her hip in a position that is just short of being inappropriate. TJ thinks, a bubble of laughter rising in her, that it's a position that might have been romantic had it not been for the fact that Rush looks so very outraged. "I hope that's all," he snarls into the radio. "Rush out."

TJ is unable to repress a giggle as she helps disentangle the two of them. It's rather ludicrous, after all, and Rush's scandalized look is hilarious, considering that _he's_ the one who's fallen all over _her_ and is still, actually, clutching her hip to regain his balance in a way she has to admit isn't entirely unwelcome. Rush pauses, removes his hand, still scowling, but his lips twitch in a way that suggests he isn't completely insensible to the ridiculousness of the situation.

"I'm sorry," TJ sputters, "it's just so, so bad-romance-novel-ish. Do you think Destiny has read the same bad romance novels I have?"

Rush cracks a smile but mutters, "I wouldn't put it past the ship."

TJ stares at him, all thoughts of humor gone. "What do you mean?" And she thinks of Carmen and she knows what he means, and she wants to cry, to scream, _Get out of my head! Stop manipulating me!_ She won't cry or scream, of course. She looks blindly at the wall.

Out of the corner of her eye she sees Rush make a swift motion towards her, then stop himself. "Are you all right?"

She sits down on a chest of equipment, schools her face to stillness, looks back at him. "I think Destiny gave me a vision, when I was shot," she says. "That my baby was -- alive. Safe. I imagine -- it was trying to protect me."

Rush breathes out, sits down beside her. "I don't, in fact, think the ship is doing anything this time, if that makes a difference," he offers. "But --" He turns his face away from her. "The ship gave me a vision of -- my wife," he says, so softly she can barely hear him.

TJ inhales sharply. His words hurt, like a flame cauterizing a wound, burning away the hope that insists on clinging, like an infection, to Carmen's loss. For if Destiny is doing the same thing to him, if it's not just her, it makes it even more probable that this explanation is the true one, that Carmen is indeed lost to her forever.

He turns to her, and at her expression, his becomes stricken, as if he understands what his words are doing to her. He probably does, she supposes. "I didn't mean -- "

She says fiercely, "I want the _truth._ That's what Destiny didn't understand."

He gingerly touches her hand in the same way she touched his earlier. "Yes. I... didn't always understand that other people on this ship could feel that way. But yes. That's it exactly."

**3\. To every action there is always an equal and opposite reaction.**

Young has been watching Rush and TJ for the past couple of weeks, ever since they got out of their quarantine-brig combination. They've been eating meals together. It's unusual for Rush to eat with anyone besides the science team, much less the same person days in a row. He's even noticed that Rush has started calling her _Tamara_ , and she calls him _Nick_. It's somewhat sickening.

Yesterday, at breakfast, TJ laughed at something Rush said. Twice. Young can't remember the last time he heard TJ laugh. He can't remember if TJ has ever laughed at something Young has said. Surely, when they were together, he was able to make her laugh. Even if he can't think of any particular incidents.

He should never have allowed them to be in quarantine-brig together, no matter that the policy has always been to quarantine in groups so no one gets too isolated. Hell, this is Rush, Rush doesn't need other people. He should have put them on opposite sides of the ship.

His subsequent talk with Rush does not go well, by even the very low standards both of them have for their talks. It very quickly disintegrates to where Young slams Rush against the wall. "What are you doing with her? God help me, Rush, if this is one of your plots, if you're trying to get back at me for something--"

"Really," Rush manages to drawl, "and here I thought this was between Tamara and me." He grabs the front of Young's uniform. "And it is," he hisses. "This is not about you. It has never been about you, don't make it about you, you pathetic excuse for a human being."

Young punches him. As usual with Rush, Young regrets what he's done the instant that it's too late. 

*

Young is unsurprised to find TJ at his door not very much later. He sighs. "Did Rush--"

"He didn't say a word to me," TJ says tightly. "He's been avoiding me, I think. In point of fact, it was Eli who talked to me."

Of course. Eli has always been a little protective of Rush when it comes to Young, ever since the planet incident.

"Okay. What are you here for, exactly?"

"Permission to speak freely, sir."

"TJ..."

"Amnesty," says TJ clearly, and for a second Young thinks she is talking about the alien. And maybe, in a way, she is. "You've -- agreed to back Nick where Destiny is concerned. Do the same personally. Don't let your -- emotional responses get in the way."

 _Nick_. God. She even sounds a little like him, although her voice is much more even than Rush has ever managed when talking to Young. With an effort he keeps his own voice level. "Is that what you came here to say?"

"Yes, sir."

"Noted. Lieutenant." He can't help but add, "If he ever hurts you--"

TJ pauses, looks at him for a long moment. Her eyes are filled with all the things she could reply -- _do you mean, if he hurts me by having an affair with me while he's still married? Or by deciding to return to his wife? Or by refusing to talk to me after our baby dies?_

She will never say these things, of course. She is much too kind for that. The only thing she says is, "You might consider me capable of taking care of myself. Sir."

Young bows his head in acquiescence.

*

Rush is not sure how long he's been working before he looks up and sees Tamara leaning against a wall, watching him. He can't remember the last time someone has watched him work -- not because she needs something from him or because she's gathering ammunition to criticize him, but just because. He looks up and smiles at her, forgetting until too late that he still has the black eye Young gave him.

She doesn't display any surprise. Eli must have told her, or Park. "I talked to the Colonel about that," she says.

Rush sighs. "I was hoping you wouldn't. It's not... relevant. I didn't want you to feel like you were the cause of it. Or that you owed me anything."

"I know," she says, making her way across the room to him. "And I know I'm not the cause, not really. I told him he has to give you -- amnesty. But, Nick, you have to do the same, you know."

Her word choice, he knows, is deliberate. He knows the alien is in her thoughts, as it is in his. If he was able to free the alien -- Young, pardoning Young for all that lies between them, should be easy. "You're right," he allows, only slightly grudgingly. "I'll try." 

She nods, accepting his answer. Rush asks, a little curious, "Did you point out to him that there's nothing between us?" Rush doesn't have to say that, out of sheer perversity, he let the other man stew in a jealousy of his own imagination. He doesn't have to say he didn't, himself, reveal to Young that he and Tamara haven't so much as touched each other since the gravity incident. The bruise on his face says it for him.

"No. It wasn't any of his business." Her eyes study his intently. "I also -- realized, while talking to him, that it wouldn't be quite honest. To say there's nothing between us, I mean." She is very close to him. It is intoxicating. "Would it?"

They're almost as close as they were when Destiny threw him into her arms. He hasn't been able to forget how her body felt. Slowly, he puts his hand on the curve of her hip, in the same place it had been then. He wonders if Destiny did, in fact, throw them together on purpose, and whether he will ever know the truth. He thinks about amnesty; about net forces, shifting between people, between aliens, through a starship; of actions and reactions.

"Tamara," he breathes in response, and their lips meet, and he stops thinking about anything else but her.

**Author's Note:**

> In Section 1, TJ quotes from the Oath of Maimonides, which is used as an alternative to the Hippocratic Oath.


End file.
